This application makes reference to and claims all benefits accruing under 35 U.S.C. Section 119 from an application entitled, xe2x80x9cDISPERSION-COMPENSATED OPTICAL FIBER AMPLIFIER,xe2x80x9d filed in the Korean Industrial Property Office on Sep. 11, 2001 and there duly assigned Serial No. 55834/2001.
1. Field of the Invention
The present invention relates to optical-communication systems and in particular to an optical-fiber amplifier disposed between an optical transmitter and an optical receiver for amplification of optical signals.
2. Description of the Related Art
In order to meet a greater demand to transmit a large amount of data in optical-communication systems, wavelength-division-multiplexing (WDM) optical-communication systems have been introduced to increase the transmission capacity. Such an increase in transmission capacity may be achieved by increasing the number of channels to be transmitted or by increasing the transmission rate of data. Currently, the data-transmission rate available in the market ranges from 2.5 Gb/s up to 10 Gb/s. To enhance a higher data-transmission rate, a number of research efforts are being made. In WDM optical-communication systems, a plurality of channels according to respective propagating modes is transmitted through a linkxe2x80x94that is, an optical fiber. However, each channel transmitted through the optical fiber is attenuated in proportion to the travel distance thereof. To address this problem, an optical-fiber amplifier is installed on the optical fiber in order to amplify the attenuated channel. Meanwhile, dispersion effects are severely increased at a transmission rate of 10 Gb/s or more. As such, dispersion-compensating fibers are also used in order to compensate for the dispersion occurring during a transmission procedure.
FIG. 1 is a view illustrating the configuration of a conventional optical-fiber amplifier and includes the first through fourth isolators 120, 160, 180, and 220; the first and second pumping light sources 140 and 210; the first and second wavelength-selective couplers 130 and 200; the first and second erbium-doped fibers 150 and 190; and, a dispersion-compensating fiber (DCF) 170.
The first isolator 120 allows an optical signal inputted to the optical-fiber amplifier to pass there-through, while cutting off an optical signal received thereto in a direction opposite that of the input optical signalxe2x80x94an optical signal received thereto via the first wavelength-selective coupler 130.
The first wavelength-selective coupler 130 couples the optical signal received from the first isolator 120 with a pumping light received from the first pumping light source 140 and outputs the resultant signal to the first erbium-doped fiber 150.
The first pumping-light source 140 pumps the first erbium-doped fiber 150, that is, it excites erbium ions in the first erbium-doped fiber 150. The first pumping-light source 140 may comprise a laser diode adapted to output a pumping light.
The first erbium-doped fiber 150 performs a forward pumping operation by the pumping light received from the first pumping-light source 140 via the first wavelength-selective coupler 130, thereby amplifying the optical signal received from the first wavelength-selective coupler 130.
The second isolator 160 allows an optical signal received from the first erbium-doped fiber 150 to pass there-through, while cutting off an optical signal received thereto in a direction opposite that of the optical signal received from the first erbium-doped fiber 150.
The DCF 170 compensates for a dispersion occurring in the amplified optical signal received from the second isolator 160. The length of the DCF 170 is determined, taking into consideration the transmission distance of the optical signal. That is, the DCF 170 has an increased length when the transmission distance of the optical signal is increased, which means the dispersion degree of the optical signal is more severe.
The third isolator 180 allows the optical signal received from the DCF 170 to pass there-through, while cutting off the optical signal received in a direction opposite to the optical signal received from the DCF 170.
The second erbium-doped fiber 190 performs a reverse pumping operation by the pumping light received from the second pumping-light source 210 via the second wavelength-selective coupler 200, thereby amplifying the optical signal received from the third isolator 180. The second erbium-doped fiber 190 serves to amplify the optical signal attenuated in intensity while passing though the DCF 170.
The second wavelength-selective coupler 200 outputs, to the second erbium-doped fiber 190, the optical signal received from the second pumping-light source 210, while outputting, to the second isolator 220, the optical signal received from the second erbium-doped fiber 190.
The fourth isolator 220 allows the optical signal received from the second wavelength-selective coupler 200 to pass there-through, while cutting off the optical signal received in a direction opposite to the optical signal received from the second wavelength-selective coupler 200.
As described above, the optical amplifier shown in FIG. 1 is equipped with the DCF 170 in order to compensate for the dispersion of the optical signal. The DCF 170 has a length proportional to the transmission distance of the optical signal. However, where the DCF 170 has an increased length, the manufacturing cost of the optical fiber amplifier increases because the DCF 170 itself is expensive.
Moreover, although the optical signal is compensated for its dispersion as it passes through the DCF 170, its intensity is reduced due to an insertion loss of the DCF 170. Accordingly, the second erbium-doped fiber 190 is arranged at the downstream end of the DCF 170 in order to amplify the attenuated optical signal. Furthermore, it is necessary to additionally use various elements such as a pumping-light source for pumping the second erbium-doped fiber 190, and a biasing circuit for driving the pumping-light source. As a result, the manufacturing cost and the volume of the optical-fiber amplifier are undesirably increased.
The present invention provides an optical-fiber amplifier capable of having an improved integration degree while being inexpensively manufactured.
In accordance with the present invention, in a wavelength-division-multiplexing optical-communication system having an optical-transmitter unit for transmitting a wavelength-division-multiplexed optical signal via an optical fiber, and an optical-receiver unit for receiving the optical signal via the optical fiber, a dispersion-compensated optical-fiber amplifier is provided. The amplifier includes a circulator for outputting an optical signal, received at a first terminal thereof connected to the optical fiber, to a second terminal thereof while outputting an optical signal received at the second terminal thereof, to a third terminal thereof connected to the optical fiber; a first amplifier for amplifying the optical signal received from the second terminal of the circulator and an optical signal reapplied thereto by utilizing an induced emission of pumped-excited ions; a dispersion-compensating fiber for compensating for a dispersion occurring in the optical signal received from the first amplifier and an optical signal reapplied thereto; a second amplifier for amplifying the optical signal received from the dispersion-compensating fiber and an optical signal re-applied thereto by utilizing an induced emission of pumped-excited ions; a splitter installed on the dispersion-compensating fiber and adapted to output, to the dispersion compensating fiber, an optical signal applied thereto and an optical signal reapplied thereto, while outputting a pumping light, applied to one end thereof and adapted to pump both the first and second amplifiers, to the other end thereof without allowing the pumping light to pass through the dispersion-compensating fiber; and, a reflector for reflecting back an optical signal received from the second amplifier, so that the reflected optical signal is sequentially reapplied to the second amplifier, the splitter, the first amplifier, and the circulator, in this order.